Planning for the Southern Pipeline began in 2005. Several different routes were considered.

The primary goal was to divert wastewater from the new southern catchments across to the Te Maunga treatment plant, because the Chapel Street plant would not be able to cope.

Southern Pipeline route selection

The route that offered the best result for the whole city was to bring the Southern Pipeline from Greerton to Memorial Park, then across the harbour to Matapihi. This option solved several wastewater network problems at once. It achieved the primary goal of diverting sewage from the southern catchments to the Te Maunga treatment plant, and it also offered more ability to relieve the overall wastewater burden that the wider city was placing on the Chapel Street treatment plant.

Independent review

In 2008 an independent review investigated the option of building a third wastewater treatment plant in the Tauriko/Lakes area instead of constructing the Southern Pipeline. The review confirmed that even with a third treatment plant at Tauriko, the Southern Pipeline still needed to be built to avoid wastewater overflows into the harbour.

The third treatment plant was more expensive than the Southern Pipeline option, with the overall cost being $47M higher than the status quo option (building the Southern Pipeline and expanding Te Maunga). It also created more problems than it solved. The biggest issue was how to dispose of the treated effluent. Options included:

pumping treated effluent into the Kopurererua Stream

building a new pipeline to carry it to the Chapel Street wastewater plant

treating it to an extremely high quality level then feeding it back into the city’s water supply network for non-drinking use only.

None of these were considered to be satisfactory options at the time. The review confirmed that even with a third treatment plant at Tauriko, the Southern Pipeline still needed to be built to avoid wastewater overflows into the harbour.